( body-lengths per second. Clumped di...)Researchers use 3-D imaging system to unveil swimming behavior of microscopic plankton

"Clumped distribution, termed 'patchiness,' is one of the most ubiquitous characteristics of oceanic zooplankton," said Genin, lead author of the Science paper. "Aggregations are found on all scales, from millimeters to hundreds of kilometers. Understanding the mechanisms that produce zooplankton patchiness is a central objective in biological oceanography."

Countless numbers of the minute, nearly transparent zooplankton are found under the surface of each square meter of the world's oceans. These animals play a key role in the marine food web as a crucial link between primary producers and predators.

The imaging system, Fish TV, uses multibeam sonar to uniquely measure animal movement. The system allowed the researchers to analyze the swimming behavior of more than 375,000 individual zooplankton swimming against vertical currents. Swimming against vertical currents allows the plankton to keep their depth, a behavior which was postulated long ago but had never been measured in the ocean until now.

The results were captured during three experiments lasting several weeks at two sites in the Red Sea's Gulf of Aqaba, near the coral reef of Eilat in Israel and at Ras Burka on the coast of Egypt's Sinai Peninsula. At the sites scuba divers attached Fish TV's sonar head ("transducer") on a large underwater tripod raised some 20 feet above the seafloor. The transducer was cabled to a control and data-acquisition unit consisting of a computer and other electronic hardware.

Fish TV's transmitters sent out 1.6 megahertz "pings" that bounced off the zooplankton and returned data to the instrument's receivers. It's a system not unlike those used in ultrasound procedures for biomedical applications.

"One of the most amazing aspects of this research is that we were able to see 375,000 of these animals, many as small as one millimeter in length," said Jaffe, a research oceanographer in the Marine Physical Labo
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Source:University of California - San Diego